JPS615603A - Antenna system - Google Patents

Abstract

PURPOSE:To reduce unnecessary radio wave radiation of the Cassegrain or parabolic antenna device by providing plural shield plates equipped with a radio wave absorber almost at right angles to a supporting pole. CONSTITUTION:The shield plates 11 are fitted at equal intervals perpendicular to the main reflection mirror axis side of the supporting pole 4, and a radio wave absorber is stuck on both surfaces of each shield plate 11. Consequently, a radio wave from a subordinate reflector 2 to the supporting pole 4 is absorbed by a radio wave absorber on a shield plate 11 and neither reaches the supporting pole 4 nor is reflected, thereby reducing unnecessary radio wave radiation. Further, a radio wave absorber is fitted to the reflector-axis side cylindrical surface of the supporting pole 4 and a plane wave 5 is absorbed and nor reflected. Consequently, unnecessary radio wave radiation is reduced.

Description

Detailed Description of the Invention [Technical Field] The present invention relates to an antenna device, particularly a support column that supports a sub-reflector or a primary radiator in a Cassegrain or parabolic aperture antenna used in microwave and sub-millimeter wave bands. The present invention relates to an antenna device that prevents deterioration of wide-angle directivity due to reflection and diffraction from the antenna.

[Prior art]

Cassegrain (or Gregorian) antennas have a structure that is almost axially symmetrical with respect to the radiation direction, and are easy to design and manufacture, so they are widely used as satellite communication earth station antennas in the microwave and quasi-mi') wave bands. . However, there is a weakness in that there are a plurality of support columns for supporting the sub-reflector in the direction of propagation of radio waves, and the reflection and diffraction of radio waves from these support columns deteriorates the wide-angle directivity. In recent years, with the development of satellite communications, the effective use of frequencies and satellite orbits has become increasingly important, and regulations against unnecessary radio wave radiation in directions other than intended, ie, requirements for wide-angle directivity, have become increasingly strict. In response to this, various methods have already been considered to improve the effects of reflection and diffraction from support columns. A method for attaching a structure (Japanese Unexamined Patent Publication No. 169905/1984) is known. However, their main purpose is to improve unnecessary radio wave radiation in a direction away from the main beam by several tens of degrees or more, which is caused by reflection and diffraction of plane waves reflected from the main reflector. The effect of reflection of radio waves directly incident on the support column from the reflector should be taken into account. According to recent analysis and detailed examination of actual measurement data, it has become clear that this effect is a factor that deteriorates the directivity in the range close to the four main beams, rather than the above-mentioned unnecessary radio wave radiation due to reflection and diffraction of plane waves. Ta.

[Purpose of the invention]

The purpose of the present invention is to eliminate the influence of reflection of radio waves directly incident on the support column from the primary radiator or sub-reflector mentioned above, and to provide a Cassegrain (including Gregorian) or parabolic beam with improved wide-angle directivity near the main beam. The present invention provides an antenna device of the form T-.

[Structure of the invention]

The antenna device of the present invention is a nine-cassegrain or parabolic antenna device comprising a support pillar that supports the sub-reflector or the primary radiator in front of the main reflector and blocks the passage of radio waves, and the support pillar has its axis aligned with the support pillar. It is constructed by providing a plurality of shielding plates extending substantially orthogonally in the mirror axis direction of the main reflecting mirror and having a radio wave absorber attached to at least the side facing the sub-reflecting mirror or the primary radiator.

[Technical background of the invention]

Next, the present invention will be described in detail with reference to the drawings. Fig. 1 is a general configuration diagram of a Cassegrain antenna, in which the main reflecting mirror 1.
Secondary reflector 2. - Consists of a secondary radiator 3 and a support column 4. In FIG. 1, the spherical wave emitted from the -order radiator 3 is reflected by the sub-reflector 2 toward the main reflector 1, reflected again by the main reflector 1, and radiated forward as a plane wave 5. Ru. A part of this plane wave is blocked by the support column 4, and the support column 4
The reflected and diffracted waves from each part of the scattering cone 6 are shown by broken lines.
It is known that the radiation is concentrated in the direction of , causing deterioration of wide-angle directivity. Secondary reflection 1
A part of the spherical wave shown by the dashed line reflected by the mirror 2 is similarly reflected by the inner cylindrical surface of the support column 4 in the direction of the cone 7, and is further reflected by the main reflecting mirror 1 to form a scattering cone. It is projected in an elliptical cone-shaped direction 8 different from 6. Unwanted radiation components due to reflection of this spherical wave have not received much attention in the past because the influences from various parts of the support column 4 in the axial direction do not necessarily add up in phase. However, it has been found that the power density is high near the sub-reflector and cannot be ignored in order to improve the wide-angle directivity near the main beam. Figure 2 is a pattern diagram showing the trajectory of unwanted radio waves in the radiation direction due to the reflection of this spherical wave, and shows an analysis example of a Cassegrain antenna that has three support pillars in an inverted Y shape arranged at equal angular intervals. ing. In Figure 2, θ is the elevation angle (EL
) t to φ represent the turning angle (A2), and the solid lines indicate the direction of unnecessary radio wave radiation due to reflection of spherical waves from each part of the support column 4.

The outer solid line 9 indicates the direction of radiation due to reflection at a portion close to the sub-reflector, the inner solid line 9' indicates the direction of radiation due to reflection at a portion close to the main reflector, and #lO indicates the scattering cone due to reflection of a plane wave. It shows the direction of 6. Assuming that the angle between the support column 4 and the radio wave radiation direction is ■, the direction of unnecessary radio wave radiation due to plane wave reflection is the maximum angle from the main beam direction, as shown in the above-mentioned Japanese Patent Laid-Open No. 169905/1983. 20, but the direction of unnecessary radio wave radiation due to reflection of the spherical wave is much closer to the main beam, and in the AZ direction φ=±(
φ1~φ2), and in the EL direction, θ=θ1~φ: and θ=
Unnecessary radio wave radiation increases between -θ3 and -04.

In the case of an earth station Cassegrain antenna with a diameter of approximately 30 m and a diameter of 0 = 46", φ!, φ11, 81, θ■, θ8.θ
4 are respectively 4°, 11.5°, 1.2°, '6.2°
tlo, 8°, 13.4° and within 15° from the main beam. Comparing the cross-polarization pattern of the earth station antenna for the Intelsat satellite using circular polarization with data measured using the satellite. Although the AZ direction pattern is symmetrical, the EL direction pattern shows asymmetry, and it is observed that unnecessary radio wave radiation increases near the above-mentioned angle, and this element cannot be ignored in order to improve wide-angle directivity. It shows. In the case of unnecessary radio wave radiation due to the reflection of a spherical wave, the number of reflections is one more than in the case of a normal radiated radio wave, so its effect on cross-polarization characteristics is noticeable, but in the case of linear polarization. The radiation characteristics of the same polarized waves deteriorate.

〔Example〕

FIG. 3 is an enlarged structural view of a part of a support column according to an embodiment of the present invention, in which shielding plates 11 are arranged at equal intervals at right angles to the main reflecting mirror axis side of the support column 4 having an oval cross section. Radio wave absorbers are attached to both sides of the shielding plate 11, respectively. As is clear from the figure, the radio waves directed from the sub-reflector toward the support column 4 are absorbed by the radio wave absorber of the shielding plate 11 and do not reach the support column 4 and are not reflected, so that unnecessary radio wave radiation is reduced. A radio wave absorber is also attached to the cylindrical surface of the support column 4 on the mirror axis side.
The plane wave 5 is also absorbed and not reflected.

As shown in the figure, the shape of the shielding plate 11 is slightly tapered at the tip to prevent interference with radio waves from increasing. Since the spherical wave from the sub-reflector has a small incident angle α, it is difficult to absorb it with a radio wave absorber attached to the cylindrical surface of the support column, but the structure of the present invention makes it easy to absorb the wave because the incident angle becomes large. be able to.

In the above example, the cross section of the support column is oval in shape, but other shapes such as a cylinder or an elliptical cylinder can be used in almost the same way, and it is explained that radio wave absorbers should be attached to both sides of the shielding plate. However, almost the same effect can be obtained without attaching a radio wave absorber to the surface on the main reflecting mirror side. Furthermore, although the shielding plates are of the same shape and arranged at equal intervals, the shape or spacing may be changed depending on the distance from the sub-reflector, and the shielding plates are not limited to being perpendicular to the support column. Furthermore, although the above description has been made regarding a Cassegrain antenna, the present invention is also applicable to a Gregorian antenna, and the present invention can be applied to a parabolic antenna in which a primary radiator is arranged at the focal position.

Furthermore, although the above embodiment has been described with the radio wave absorber attached to the support punch itself, it is possible to improve unnecessary radio wave radiation near the main beam even without the radio wave absorber on the support punch itself. , this does not preclude the use of other conventional methods in combination to improve unnecessary radio wave radiation in directions away from the main beam.

〔Effect of the invention〕

As explained in detail above, according to the antenna device of the present invention, the shielding plate is provided almost at right angles to the support column, and the radio wave absorber is attached to the sub-reflector or the primary radiator side, so that the shielding plate is close to the main beam. It is possible to improve the unnecessary radio wave radiation characteristics of angularly polarized waves (in the case of linearly polarized waves) or cross-polarized waves (in the case of circularly polarized waves), which is effective in reducing interference between satellite systems.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram showing the general configuration of a Cassegrain antenna, Fig. 2 is a pattern diagram showing the radiation direction of unnecessary radio wave radiation from a support column, and Fig. 3 shows a part of a support column according to an embodiment of the present invention. It is an enlarged structural diagram. 1...Main reflecting mirror, 2...Sub reflecting mirror, 3...
...-Next radiator, 4...Support column, 5...
・Plane wave, 6... Scattering cone, 11... Shielding plate. XL, -'=. Figure 1 Figure 2 θ

Claims (1)

[Claims] In a Cassegrain or parabolic antenna device equipped with a support column that supports a sub-reflector or a primary radiator in front of a main reflector and blocks the passage of radio waves, the support column is substantially orthogonal to the axis of the main reflector, and the main reflector is An antenna device comprising a plurality of shielding plates extending in the mirror axis direction of the mirror and having radio wave absorbers attached to at least the side facing the sub-reflector or the primary radiator.